The invention relates to a continuously operating press for the production of particle boards, fiber boards or similar wood boards and plastic boards.
Designs for such continuously operating presses have been disclosed by German Offenlegungsschrift/Patent 2,157,746, 2,545,366, 3,133,817, 3,914,105 and German Utility Model 7,525,935.
To control the procedure, all continuously operating presses must precisely reproduce the process sequence, as is known from the known intermittent-operation press technology for the production of particle boards, MDF boards (Medium Density Fiber) or OSB boards (Oriented Strand Boards). For this purpose, it is necessary that all continuously operating presses should be capable of deforming at least one press/heating platen, either the upper or the lower one, spherically in the longitudinal and transverse directions in such a way that relatively large distances or nip clearances between the upper and the lower heated press platen can be set longitudinally in accordance with the different thicknesses of the boards to be produced, their moisture content and the resulting steel-belt speeds or, in other words, production rates, to give the necessary uniform steam distribution or degasification along the pressing zone. The same applies to a transverse deformation of the press/heating platen, this being essentially a convex action on the pressing stock, this having a favorable effect for example on the transverse tensile strength and, in association with this, also on the consumption of adhesive.
This object is achieved to greater or lesser degrees by all existing continuously operating presses, that is to say with a greater or lesser time requirement for a change in the process parameters for this.
In the case of the presses disclosed in German Patents 3,133,817 and 3,914,105, the spacings between the frames are chosen in such a way that the heating platens in conjunction with the slab are relatively thick. In the case of the press in accordance with German Patent 3,133,817, a counter heating facility is integrated into the slabs and, in accordance with German Patent 3,914,105, into the heating platens. By means of these counter heating facilities, the heating platens can be deformed concavely, in a plane-parallel manner or convexly. When there is a change in production, from a thick board (38 mm) to a thin board (8 mm) for example, the convex transverse deformation and the temperature profile must be changed. Due to the combined thickness of the press/heating platen and the slab with its counter heating facility, the system operates relatively slowly. In order to accelerate the transverse deformation processes somewhat, the forces of the outer cylinders are changed with respect to the pressing cylinders arranged in the center. Due to the thickness of the heating and slab system, on-line adjustment, i.e. in the course of a change effected without interrupting production, by means of this change in the force in the cylinders is possible to only a limited extent, up to about 40%. Extreme changeovers from thick- to thin-board production are therefore only accomplished, if at all, by interrupting maintenance shifts--which can last for several hours--because the thermal changes require this time.
In the case of the presses from German Offenlegungsschrift 2,157,746, German Offenlegungsschrift 2,545,366 and German Utility Model 7,525,935, each frame is assigned a multiplicity of pressing cylinders, allowing any desired spherical deformation of the press/heating platen to be carried out in the longitudinal and transverse directions. To this extent, such a press meets the requirement for an on-line adjustment in a change effected without interrupting operation. However, the outlay in terms of constructing the machinery is considerable since the concept, which uses a relatively thin press/heating platen, requires a very narrow spacing between the frames, which means a large number of frames and hence also a large number of hydraulic actuating cylinders i.e. almost a carpet of bottom pistons. This concept involves relatively high production costs.
The requirement made of modern systems, however, is for just-in-time production, i.e. flexible manufacture according to orders. This means that a continuously operating press must be capable of carrying out a change without interrupting operation. The continuously operating presses known on the market at present can only do this to a limited extent or, in some cases, not at all.
The continuously operating presses constructed by the applicant hitherto operate on the principle of a lateral-arrangement top-piston press for the longitudinal influencing of the upper heating platen so as to deform the press along the pressing zone and with the additional arrangement of multi-pot/hydraulic short-stroke cylinders which are installed centrally underneath the lower heating platen for the purpose of transverse deformation. The principle of the press frame of this continuously operating press is known from Patent Application German Offenlegungsschrift 4,017,791. This embodiment of a continuously operating press is capable of setting the respective spherical deformation of the press/heating platen in the longitudinal and transverse directions in an on-line process in which the change in production is carried out without interrupting operation. However, the outlay in terms of constructing the machinery and the resulting production costs for this kind of continuously operating press is considerable, particularly due to the design of the press ram system with the associated arrangements of the laterally attached top pistons.
The use and development of continuously operating presses has led in recent years to continuously rising production rates, leading to press lengths in the region of 40 m and more. This was associated with a dramatic increase in the number of hydraulic actuators along the pressing zone to set the pressing-force profile longitudinally and transversely, forming a so-called hydraulic carpet of cylinder-pistons. The same applies to the press/heating platens and to the operating wear in the region of rolling support. An increase in the length of the press brings with it an increase in the speed of the steel belts and thus in the rolling speeds of the rolling supporting elements (rolling rods or rolling chains), thereby shortening the life expectancy of the wear-dependent functional elements. All this leads to an increased susceptibility to faults, with the result that there is the inevitable requirement in such complex plant systems that the hydraulic actuators should be rapidly accessible for maintenance and/or repair in the case of a fault and that wearing elements (heating-platen or rolling-contact plate systems) should be rapidly replaceable.
This is not readily possible in the case of the two first-mentioned press-frame arrangements in accordance with German Patent 3,133,817 and German Patent 2,157,746 since the window-frame construction or beam construction prevents direct access from the side. Replacement or removal of the hydraulic actuators at the side, e.g. changing the hydraulic sealing elements, is associated with a considerable investment of time, that is with fairly long interruptions to production. The situation is even more critical as regards the replacement of the functional members subject to wear, that is the press/heating platens. Here, the steel belts must be taken apart in order to replace these heating platen/rolling-contact systems at the end, either at the entry or exit end. This replacement can require up to several weeks and obviously entails not only a massive financial loss for the operator but also possibly a poor reputation resulting from overlong delivery times.